Regarding the Solid 7 + Elpico combinaton, I tried to explain the sound in my article. I will try to translate that piece in English for you:

"...There were units with one, two or three pickups, being the one fitted on Paul McCartney’s guitar the two pickups unit, which had the commercial name of PP-2. The four knobs served as volume and tone, two for each of the pickups.

As for the sound, and taking into account that no recording of Paul McCartney playing his Rosetti Solid 7 guitar is known to have survived, the following comments refers to a test made with the named guitar, belonging to a private collection, plugged into an Elpico AC-52 amp, and taking into account that these type of tests have always a very subjective component, for reasons that are not necessary to explain. Using only the neck pickup, the guitar has a ‘hot’ tone, a feature that is enhanced by the semihollow body. If the tone knob is put counterclockwise, the sound becomes more ‘obscure’ and dully. If the bridge pickup is used, the sound tends to feed back, and a ‘trebly’ tone comes out of the amp. Putting the tone knob of the bridge pickup counterclockwise, the feedback disappears and the sound becomes less strident. Blending both pickups, gives the full potential of the guitar sound, something that can be understood in terms of using the guitar as a ‘rhythm_rock_and_roll’ one: full sound, plenty of harmonics and with high output signal.

In conclusion, and although the guitar can’t be ranged as a top one, the sound coming out of it can be catalogued as a ‘full one’, that sounds like more as a semisolid guitar -for example, like an Epiphone Casino- than as a solid one. The “...piece of crap...” as Paul McCartney used to refer to, was more in consonance with its playability -fat neck, high action, misalignments in the tuning- than in the sound itself..."